There is a beautiful discussion at HispaLUG about the toxicity of Lego for fish. So curiosity came to my mind, and I made a quick google search for Lego Aquariums. This is the result:

I have never been interested in aquariums, but I thought it could be a cool idea to make “water gadgets” for aquariums out of Lego. That was the reason for my search. The two Lego Aquariums above are really original.

Oh! And apparently Lego Plastic (ABS) is not toxic for fishes. So don´t doubt, if you have an aquarium and love lego, try something new ;).